“Early in the third set I hit one serve and I never felt the same after that,” Kyrgios said. “Something didn’t feel right in my arm.”

There were 87 matches on Wednesday’s agenda after 55 rain postponements from Tuesday as the first round concluded and second began on the New York hardcourts.

Sharapova, ranked 146th, fired 12 aces with 39 winners and 36 unforced errors. She played only one Open tuneup match due to a forearm injury but wore down Halep and Babos to show everyone she is truly a threat for a deep run.

Sharapova dropped the last two tie-break points on errant forehands to hand Babos the first set. Sharapova broke to open the second, double faulted away a break in the fourth game, then broke again in the seventh and held twice to force a third set.

“In the second set I felt like I was physically fresh and that gave me a lot of confidence,” Sharapova said. “I just wanted to be the fittest player out there in the end and I think I was.”

Sharapova broke to open the third set and again for a 4-1 edge when Babos netted a forehand drop volley and again on match point when Babos sent a backhand wide.

Kyrgios, 22, beat Rafael Nadal two weeks ago on the way to the biggest final of his career at the ATP Cincinnati Masters before falling to Grigor Dimitrov.

Kyrgios grabbed his right shoulder after a serve in the fourth game of the third set, having a ballboy grab his right arm to try and ease the pain at one stage.

Kyrgios then told a physiotherapist his woes during a medical timeout.

“One serve and arm is totally dead. It’s so dead and numb. It’s incredibly weak,” said Kyrgios. “How can something happen all of a sudden? I wasn’t feeling it at all and then Bang, one serve. I lost power in my serve.”

After his last available treatment, Kyrgios dropped eight of the last nine games to Millman, back after missing nearly eight months with a hip injury.

“Nick’s shoulder deteriorated as the match went on,” Millman said after his first US Open triumph. “It’s a victory but slightly hollow.

“He’s a teammate. He’s a great guy on and off the court. I feel for him. I really do.”

Austrian sixth seed Dominic Thiem finished off Australian Alex de Minaur 6-4, 6-1, 6-1. The two-time French Open semi-finalist is the highest-ranked rival to Federer and Nadal on their side of the draw.

“I’m not in the first row of favorites, maybe in the second, so I can play calm,” Thiem said.

Kuznetsova is among seven women who could become world number one after the US Open. So is Ukraine’s fourth-seeded Elina Svitolina, who held off 42nd-ranked Czech Katerina Siniakova 6-0, 6-7 (5/7), 6-3.

Svitolina dropped six of nine tie-breaker points when her match resumed but battled through the third set into the second round. --AFP